Auditory stream segregation, the organization of sounds arriving at the ear into meaningful perceptual events or 'streams,' is a process involving pre-attentive mechanisms that operate very early in auditory processing. Since higher-order processes operate on these streams, auditory stream segregation is a crucial stage in auditory processing. Understanding how the auditory system performs auditory stream segregation requires an understanding of the neural and molecular mechanisms involved. Although many vertebrates beside humans demonstrate auditory stream segregation, none of these systems have provided significant advances in our understanding of the underlying neural mechanisms. Katydids (an insect) also perform auditory stream segregation, but it occurs at the level of a single auditory neuron called TN-1. TN-1 responds selectively to slow pulse rates while responses to high pulse rates are suppressed; however, if both pulse rates are presented simultaneously at different carrier frequencies, TN-1 will continue to respond to slow rate pulses, but not fast rate pulses. All evidence indicates that the mechanisms responsible are intrinsic to TN-1. Dr. Schul and I propose the dynamic compartmentalization hypothesis to explain auditory stream segregation in TN-1: suppression is localized to tonotopically organized TN-1 dendritic regions activated by the frequencies contained in fast pulse rate stimuli while non-stimulated regions remain sensitive to auditory input from other frequencies. The proposed experiments provide the initial steps for establishing TN-1 as testable model system for studying the neuronal, and eventually behavioral and molecular mechanisms of auditory stream segregation by determining: 1) whether high pulse rates cause a decrease in input resistance in TN-1 (which mediates the suppression of TN-1 responses) and whether sodium and/or calcium mediates this decrease using intracellular recording and stimulation of TN-1 dendrites, and 2) whether suppression is restricted to dendritic regions activated by fast pulse rates (i.e., dynamic compartmentalization hypothesis) through intracellular recordings of TN-1 dendrites and imaging of sodium and/or calcium in TN-1 dendrites. Many human communicative disorders,, as well as some mental disorders, such as schizophrenia, involve information processing deficits. Although higher-order processes are certainly involved, an inability to successfully separate incoming auditory information into meaningful streams would contribute to deficits in auditory processing at higher levels. A working model system involving the katydid TN-1 auditory neuron could also serve a secondary purpose as a system for examining how information processing can be disrupted. [unreadable] [unreadable] [unreadable]